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26 PERSPECTIVE.
Fig. be done, by the rules for upright pidures, lines muft
18. be drawn from the top Q to the geometrical plane,parallel to SX, as Dm. Then by having the length of
tnD, the image of D may be found; and then the
image of M, and the flolid compleated.
Scholium.
Hitherto I have been laying down fuch principles as are the foundation of the whole practice of
perfpedive; which being well underftood, the reafon of the feveral operations in the pradice will eafily be fhewn and made intelligible.
And tho' objeds may be drawn in perfpedive
various ways, either upon a plane perpendicular to
the horizon, or parallel to it, or inclined t in any
given angle; yet fince almoft all objeas ftand perpendicular to the horizon, and all views and perfpeaive draughts, are hung againft a wall, which
is alfo perpendicular to the horizon. And fince
the rules for drawing are the moft fimple and eafy,
when the piaure is in that pofition. Therefore I
have given all the principles in full for that fort of
projection. And in order to extend the rules to
other kinds, I have given fome propofitions, fhew-
ing how the other forts may be reduced to this.
Alfo as it is moft natural to look at a draught of
any thing diredly, rather than obliquely. And
all towns, cities, caftles, towers, churches, edifices
of all forts, ftand in a perpendicular pofition, this
fort muft be efteemed the moft natural of any, as
well as the moft ready, familiar, and eafy.
And tho' the objeds I have been defcribing,
are fuch as fall below the horizontal line, and beyond the pidure. Yet all the propofitions are
equally true, tho' the objeds are never, fo high;
or when they are between the eye and the pidure.
But to have drawn them fo, would have required
larger figures and more room.
And

26 PERSPECTIVE.
Fig. be done, by the rules for upright pidures, lines muft
18. be drawn from the top Q to the geometrical plane,parallel to SX, as Dm. Then by having the length of
tnD, the image of D may be found; and then the
image of M, and the flolid compleated.
Scholium.
Hitherto I have been laying down fuch principles as are the foundation of the whole practice of
perfpedive; which being well underftood, the reafon of the feveral operations in the pradice will eafily be fhewn and made intelligible.
And tho' objeds may be drawn in perfpedive
various ways, either upon a plane perpendicular to
the horizon, or parallel to it, or inclined t in any
given angle; yet fince almoft all objeas ftand perpendicular to the horizon, and all views and perfpeaive draughts, are hung againft a wall, which
is alfo perpendicular to the horizon. And fince
the rules for drawing are the moft fimple and eafy,
when the piaure is in that pofition. Therefore I
have given all the principles in full for that fort of
projection. And in order to extend the rules to
other kinds, I have given fome propofitions, fhew-
ing how the other forts may be reduced to this.
Alfo as it is moft natural to look at a draught of
any thing diredly, rather than obliquely. And
all towns, cities, caftles, towers, churches, edifices
of all forts, ftand in a perpendicular pofition, this
fort muft be efteemed the moft natural of any, as
well as the moft ready, familiar, and eafy.
And tho' the objeds I have been defcribing,
are fuch as fall below the horizontal line, and beyond the pidure. Yet all the propofitions are
equally true, tho' the objeds are never, fo high;
or when they are between the eye and the pidure.
But to have drawn them fo, would have required
larger figures and more room.
And